As a promising treatment for type 1 diabetes, pancreatic islet transplantation still faces several challenges, including autoimmune diabetes recurrence and alloreactive rejection. Long-term use of general immunosuppressants prolongs the survival of transplanted islets, but also brings the risk of tumorigenesis and infections, and suppresses the function of grafted islets. Gene therapy delivers therapeutic genes into cells and modifies cellular functions. Recently, we have demonstrated the ability of using a recombinant adeno-associated virus (rAAV) encoding viral IL-10 (vIL-10) gene to prevent diabetes in nonobese diabetic (NOD) mice. We showed that expression vIL-10 gene reduces circulating levels of IL-2 and INF-g and prevents islet destruction in NOD mice. In this application, we hypothesize that systemic delivery of vIL-10 using an AAV vector may reduce immune response and suppress destruction of transplanted islets in vivo. We propose to test the ability of AAV vIL-10 to prevent autoimmune diabetes recurrence in NOD recipients after syngeneic islet grafting; and to improve graft survival after allogeneic islet transplantation. In this study, we will systemically deliver AAV vIL-10 to diabetic NOD recipients prior to syngeneic islet grafting. The prolonged survival of transplanted syngeneic islets in NOD recipients will indicate vlL-10's ability to suppress autoimmune recurrence. We will implant MHC-incompatible B6AF1 mouse islets into diabetic NOD recipients with systemic MV vIL-10 treatment to assess the possibility of preventing alloreactive rejection. The prolongation of allogeneic islets will suggest the induction of immune unresponsiveness in recipients. We will not only monitor the survival and function of the transplanted islets, but also study kinetics of the vIL-10 transgene expression and cytokine profile in recipients. Use of a vIL-10 neutralizing antibody and nephrectomy of islet-implanted kidneys will conform the vlL-10-dependent protection and the sole source of insulin from islet grafts in recipients respectively. Histological and immunohistochemical examinations of islet grafts will aid the mechanistic elucidation of the immunoregulative effect of vIL-10. This study will provide an experimental strategy of using AAV vlL-10 gene therapy to investigate immunosuppression induction in islet transplantation.